1. Field of the Invention
The present invention is generally directed to safety equipment used in elevator systems and more particularly, the present invention is directed to an improved safety system using modem electronic components. The improved safety system greatly improves installation time, quality, manufacturing costs, and operational characteristics.
2. Prior Art
State of the art elevator safety systems are implemented using a Safety Chain which is a serial circuit comprised of switches and contacts. The contacts and switches are operated by the service person and some devices in the elevator. Some devices are controlled by the car such as the overspeed governor, and the limit switch. Others are controlled by the doors, such as the switches and the locks of the landing doors.
The Safety Chain operates relays (or contactors) that handle the power to the motor and the brake. An operation of any contact within the chain will disconnect the motor or drive from the main power supply. Some parts of the Safety Chain might be bridged, other parts might be included to alternate the safety supervision for special modes during inspection, maintenance and rescue operation.
During maintenance and inspection, it is sometimes necessary to include bridges in the Safety Chain by hand for testing and error searching. The bridges may be located throughout the hoistway and car. Manual installation and removal of the bridges is time and labor intensive.
The serial connections of the contacts and the bridging and including of contacts for rescue operation and inspection lead to a long chain which is usually several times (usually six to eight) the length of the hoistway. The length of the Safety Chain leads to the usage of higher voltages in the range of the main voltage to minimize the effects of voltage losses along the chain.
The contacts in the Safety Chain must have a positive opening characteristic. The use of electronic sensors is not allowed in many installations.
Up until very recently, almost all countries required that elevator safety systems be mechanically implemented because of concerns that electronic implementations would be incapacitated by power failures. Regulations have changed, however, in light of the recognized ability of electronic engineers and improved technology. These new designs provide for a fail safe mode in the event of power failures.
Therefore it has been determined that a need exists for an improved design of an elevator safety system which lowers part count and manufacturing costs, all while improving operability.